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Abstract Farming of Amazonian native fish species holds great promise. One species whose characteristics make it suitable for intensive farming is tambaqui (Colossoma macropomum). However, there is a lack of consensus about the most suitable stocking density (SD) for intensive farming. More information on the physiology of fish in farming systems is thus required, as this would increase our understanding of the effects of stress on these fish. The aim of this study was therefore to evaluate the effect of different SDs on the hematology and plasma protein profile of tambaqui. To this end, juvenile tambaqui were exposed to the following different SDs (kg/m3) for 96 h: SD1 = 2.11; SD2 = 8.31; SD3 = 16.34; and SD4 = 27.40. Water quality was monitored, and blood was collected for hematological analysis and electrophoresis (SDS-PAGE) to analyze plasma protein and immunoglobulin profiles. Gill filaments were removed and the number of parasites (monogenoids) was counted. Multivariate PCA analysis revealed a strong positive association between the highest SDs (SD3 and SD4) and parasite count, immune cells (eosinophils, thrombocytes, monocytes and lymphocytes) and water ammonia and nitrite levels. Conversely, the highest SDs were negatively associated with water quality variables (pH, turbidity, conductivity and O 2 content) and blood hematocrit. The results show that the highest SDs contributed to a deterioration in water quality, leading to increased MetHb levels, gill parasitism, an increase in the number of defense cells, altered protein profile and stimulation of immunoglobulin production. These changes suggest that the welfare of tambaqui is adversely affected by high SDs and increase our understanding of the effects of crowding stress on the physiology of the species. Short note Adequate stocking density (SD) of farmed fish is one of the most important factors affecting the welfare of these animals. Tambaqui (Colossoma macropomum) is the most widely bred fish in the Amazon region. There is no information about the physiological effects of SD on this species. We found that increased SD leads to changes in water quality and hematology of C. macropomum , SD3 (16.34 kg/m3) and SD4 (27.40 kg/m3) being the densities that resulted in the greatest changes. The combined effect of a deterioration in water quality, particularly in terms of nitrogenous waste, and increased SD must have played an important role in the physiological changes observed. The highest densities are very closely associated with induction of cellular immunity in the fish. Under these circumstances, the plasma protein profile changes, producing effects that are probably harmful to the welfare of intensively farmed fish. Highlights • Tambaqui reared at higher stocking density (16-27 kg/m3) showed physiological changes and the quality of water was lost. • The physicochemical parameters of the water and the physiological parameters of the fish were combined in a PCA analysis. • The leukocytosis and thrombocytosis observed here were strongly correlated with the number of gill parasites. • Highest SDs contributed to a stimulation of immunoglobulin production. [ABSTRACT FROM AUTHOR]

Abstract: Injuries caused by freshwater stingrays are characterized by intense pain and pathological changes at the lesion site, including oedema, erythema and, in most cases, necrosis. In this study, the systemic myotoxic activity induced by mucus extracts from the dorsal region and stinger of the stingrays Plesiotrygon iwamae and Potamotrygon motoro was described, analysed and quantified. Twenty-four hours after injection of 400 μg of the extracts into the gastrocnemius muscle of mice, the following effects were observed: coagulative necrosis of the muscle tissue, muscle fibre regeneration and the presence of inflammatory infiltrates, including neutrophils, macrophages, and a reduced number of eosinophils and lymphocytes. These changes were also observed, although to a lesser extent, in the gastrocnemius muscles of the contralateral limbs, demonstrating that the extracts from the two species could induce systemic rhabdomyolysis. Based on morphometric analysis, it was observed that the stinger extract of P. motoro was more potent in inducing local and systemic myotoxic activity, followed by the dorsal extract from P. motoro and stinger and dorsal extracts from P. iwamae, which induced similar effects. [Copyright &y& Elsevier]